Optical reduction system with control of illumination polarization

ABSTRACT

An optical reduction system with polarization dose sensitive output for use in the photolithographic manufacture of semiconductor devices having variable compensation for reticle retardation before the long conjugate end. The variable compensation component(s) before the reticle provides accurate adjustment of the polarization state at or near the reticle. The variable compensation components can be variable wave plates, layered wave plates, opposing mirrors, a Berek&#39;s compensator and/or a Soleil-Babinet compensator. The catadioptric optical reduction system provides a relatively high numerical aperture of 0.7 capable of patterning features smaller than 0.25 microns over a 26 mm×5 mm field. The optical reduction system is thereby well adapted to a step and scan microlithographic exposure tool as used in semiconductor manufacturing. Several other embodiments combine elements of different refracting power to widen the spectral bandwidth which can be achieved.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to optical systems used insemiconductor manufacturing.

[0003] 2. Related Art

[0004] Semiconductor devices are typically manufactured using variousphotolithographic techniques. The circuitry used in a semiconductor chipis projected from a reticle onto a wafer. This projection is oftenaccomplished with the use of optical systems. The design of theseoptical systems is often complex, and it is difficult to obtain thedesired resolution necessary for reproducing the ever-decreasing size ofcomponents being placed on a semiconductor chip.

[0005] Therefore, there has been much effort expended to develop anoptical reduction system capable of reproducing very fine componentfeatures, less than 0.25 microns. The need to develop an optical systemcapable of reproducing very fine component features requires theimprovement of system performance.

[0006] A conventional optical system is disclosed in U.S. Pat. No.5,537,260 entitled “Catadioptric Optical Reduction System with HighNumerical Aperture” issued Jul. 16, 1996 to Williamson, which isincorporated by reference herein in its entirety. This referencedescribes an optical reduction system having a numerical aperture of0.35. Another optical system is described in U.S. Pat. No. 4,953,960entitled “Optical Reduction System” issuing Sep. 4, 1990 to Williamson,which is incorporated by reference herein in its entirety. Thisreference describes an optical system operating in the range of 248nanometers and having a numerical aperture of 0.45.

SUMMARY OF THE INVENTION

[0007] While these optical systems perform adequately for their intendedpurpose, there is an ever increasing need to improve system performance.The present inventor has identified that a need exists for minimizingthe effects of reticle birefringence. Further, there is a need for anoptical system having low linewidth critical dimension (CD) controlerrors capable of acceptable system performance.

[0008] The introduction of compensation to control illuminationpolarization limits the performance impact of reticle birefringence onpolarization sensitive projection optics including catadioptricprojection optic. When the reticle substrate exhibits birefringencethere will be a change in the polarization of the light projectedthrough the optical system.

[0009] This change alters the performance of the entire system.Characteristics such as reflectivity, insertion loss, and beam splitterratios will be different for different polarizations. This leads to doseerrors at the wafer. Dose errors contribute toward linewidth CD controlerrors.

[0010] Furthermore, even for a perfectly preferred polarization, doseerrors can occur from reticle birefringence. This effect will berelatively small, but if the reticle substrate exhibits birefringenceand the input light has a small error in it, then the dose errors willbe much greater. The present invention minimizes the effect of reticlebirefringence by optimizing the illumination by making very smallchanges to the illumination polarization based on the input light. Doseerror is thereby minimized. This minimization results in a reduction inlinewidth CD control error.

[0011] In one embodiment, a catadioptric optical reduction system has avariable compensation for reticle retardation before the long conjugateend. The variable compensation component(s) before the reticle providesadjustable elliptically polarized light at or near the reticle. Thevariable compensation components can be variable wave plates, reflectiveor transmissive thin film polarizers, a Berek's compensator and/or aSoleil-Babinet compensator.

[0012] In some applications, the reticle has small amounts, much lessthan a wavelength, of birefringence. In such applications, thebirefringence varies over the reticle. This varying birefringence altersthe desired polarization state introducing dose errors and associated CDlinewidth variation that are a function of position.

[0013] The polarization compensator allows for optimization of theillumination polarization state to minimize the dose errors. These smallchanges adjust the polarization purity to a better level of perfectionin comparison to the few percent polarization purity traditionallyrequired in optical systems.

[0014] The polarization state purity is adjusted by making small changesto the actual polarization ellipticity. In general, the compensator canbe located at anywhere in the illumination system to change thepolarization state at the reticle.

[0015] However, if there are any strong polarizers (for example,polarization analyzers), then the compensator should be located in thereticle side of the polarizers.

[0016] The catadioptric optical reduction system provides a relativelyhigh numerical aperture of 0.7 capable of patterning features smallerthan 0.25 microns over a 26 mm×5 mm field. The optical reduction systemis thereby well adapted for photolithographic applications and tools,such as a step and scan microlithographic exposure tool as used insemiconductor manufacturing. Several other embodiments combine elementsof different refracting power to widen the spectral bandwidth which canbe achieved.

[0017] In another embodiment, the present invention is a catadioptricreduction system having, from the object or long conjugate end to thereduced image or short conjugate end, a polarization compensator, areticle, a first lens group, a second lens group, a beamsplitter cube, aconcentric concave mirror, and a third lens group. The concave mirroroperates near unit magnification. This reduces the aberrationsintroduced by the mirror and the diameter of radiation entering thebeamsplitter cube. The first and second lens groups before the concavemirror provide enough power to image the entrance pupil at infinity atthe aperture stop at or near the concave mirror. The third lens groupafter the concave mirror provides a substantial portion of the reductionfrom object to image of the optical system, as well as projecting theaperture stop to an infinite exit pupil. High-order aberrations arereduced by using an aspheric concave mirror.

[0018] Further embodiments, features, and advantages of the presentinvention, as well as the structure and operation of the variousembodiments of the present invention, are described in detail below withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

[0019] The accompanying drawings, which are incorporated herein and forma part of the specification, illustrate the present invention and,together with the description, further serve to explain the principlesof the invention and to enable a person skilled in the pertinent art tomake and use the invention.

[0020] In the drawings:

[0021]FIG. 1 is a schematic illustration of a conventional opticalprojection system.

[0022]FIG. 2A is an illustration of the birefringent properties of areticle.

[0023]FIG. 2B is an illustration of the properties of a Berek'scompensator.

[0024]FIG. 2C is an illustration of the properties of a Soleil-Babinetcompensator.

[0025]FIG. 3 is a schematic illustration of one embodiment of thepresent invention using a Berek's compensator.

[0026]FIG. 4 is a schematic illustration of one embodiment of thepresent invention using a Soleil-Babinet compensator.

[0027]FIG. 5 is a schematic illustration of a further embodiment of thepresent invention using a single refracting material.

[0028]FIG. 6 is another embodiment of the present invention using twodifferent refracting materials.

[0029]FIG. 7 is another embodiment of the present invention using morethan two different refracting materials.

[0030]FIG. 8 is another embodiment of the present invention.

[0031]FIG. 9 is yet a further embodiment of the present invention.

[0032] The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements. Additionally, the left-mostdigit(s) of a reference number identifies the drawing in which thereference number first appears.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Table of Contents

[0033] I. Overview

[0034] II. Terminology

[0035] III. Conventional Optical System and Reticle Birefringence

[0036] IV. Polarization Compensation

[0037] V. Example Implementations

[0038] A. Optical System With Control of Laser Illumination Polarization

[0039] B. Alternate Embodiment

[0040] C. Further Embodiments

[0041] I. Overview

[0042] The present invention compensates for reticle birefringence. Thiscan improve the imaging quality of catadioptric reduction systems inphotolithography. To describe the invention, a terminology section isfirst provided. An overview section follows that describes an exampleconventional optical reduction system (FIG. 1) and the problem ofreticle birefringence recognized by the present inventor (FIG. 2A).Polarization compensation and optical components for accomplishingpolarization compensation according to the present invention aredescribed (FIGS. 2B and 2C). Finally, example implementations of thepresent invention that have one or more compensators in opticalreduction systems to improve imaging quality are discussed (FIGS. 3-9).

[0043] II. Terminology

[0044] To more clearly delineate the present invention, an effort ismade throughout the specification to adhere to the following termdefinitions as consistently as possible.

[0045] The term “circuitry” refers to the features designed for use in asemiconductor device.

[0046] The term “dose error” refers to variations in the powerdistribution of radiation incident on the image or wafer plane.

[0047] The term “feature orientation” refers to the patterns printed ona reticle to projection.

[0048] The term “long conjugate end” refers to the plane at the objector reticle end of the optical system.

[0049] The term “short conjugate end” refers to the plane at the imageor wafer end of the optical system.

[0050] The term “print bias” refers to the variations in the lines onthe wafer produced by asymmetries in the optical system. Asymmetries areproduced by diffraction at various stages of the system and the reticle.

[0051] The term “semiconductor” refers to a solid state substance thatcan be electrically altered.

[0052] The term “semiconductor chip” refers to a semiconductor devicepossessing any number of transistors or other components.

[0053] The term “wafer” refers to the base material in semiconductormanufacturing, which goes through a series of photomasking, etchingand/or implementation steps.

[0054] The term “wave plate” refers to retardation plates or phaseshifters made from materials which exhibit birefringence.

[0055] III. Conventional Optical System and Reticle Birefringence

[0056]FIG. 1 illustrates a conventional optical reduction system. Fromits long conjugate end where the reticle is placed to its shortconjugate end where the wafer is placed, it possesses a first opticalcomponent group 120, a beamsplitter cube 150, a first quarter-wave plate140, a concave mirror 130, a second quarter-wave plate 160, and a secondoptical component group 170. Each of these components 120-170 aredescribed further in U.S. Pat. No. 5,537,260 entitled “CatadioptricOptical Reduction System with High Numerical Aperture” issued Jul. 16,1996 to Williamson (incorporated herein by reference). A feature of anyoptical system is the interdependence of numerical aperture size andspectral radiation requirements. In order to efficiently illuminate thereticle, linearly polarized light may be desired. In some cases, otherillumination polarization states, for example right or left handcircular polarization, may be desired. The limitations of linearly ornearly linearly polarized light are introduced above and discussed inthe following sections.

[0057] As recognized by the present inventor, most all reticles areweakly birefringent. Thus, reticles alter the linearly polarized lightbeing used to project from the reticle to the wafer. Much as a waveplate, but to a much smaller degree, a reticle can elliptically polarizeincident linearly polarized light. This introduces dose errors at thewafer which are magnified at least in part by feature orientations onthe reticle. Dose errors contribute to linewidth CD control errors evenfor a preferred polarization. Linewidth CD control errors aredetrimental to the performance of semiconductor devices.

[0058]FIG. 2A illustrates the birefringent properties of reticle 110.Reticle 110 is placed in the path of linearly polarized light 210. Thevector diagram 205 illustrates the linear state of polarization. Reticle110 is a weak retarder, that is, it exhibits a small amount ofbirefringence. After reticle 110, the light is polarized differently, asshown by the curves in light output 230. The vector diagram 235 showsthe tip 237 and spread 238 of the light leaving the reticle.

[0059] IV. Polarization Compensation

[0060] Wave plates (retardation plates or phase shifters) are made frommaterials which exhibit birefringence. Birefringent materials, includingglassy materials under internal or external stress and crystals, aregenerally anisotropic. This means that the atomic binding forces on theelectron clouds are different in different directions and as a result soare the refractive indices.

[0061] The simplest class of crystals are those with cubic symmetry. Ina cubic crystal, all three crystallographic directions or axes areequivalent. n_(x)=n_(y)=n_(z), and the crystal is optically isotropic.Regardless of how the light is polarized with respect to the crystal, itwill experience the same refractive index and hence phase delay.Therefore, any polarized light, aside from accumulating a constant phasedelay, remains unchanged after traveling through a defect-free,isotropic crystal. (This is also true for amorphous substances likeglass.)

[0062] However, another class of crystals exhibits asymmetric (oranisotropic) optical properties. They are known as birefringentcrystals. One birefringent type is uniaxial, meaning that one crystalaxis is different from the other two: n_(z)≠n_(x)=n_(y). Common uniaxialcrystals of optical quality are quartz, calcite and MgF₂. The singlecrystal axis that is unique is often called the “extraordinary” axis,and its associated refractive index is labeled n_(e), while the othertwo axes are “ordinary” axes with index n_(o).

[0063] In the case of uniaxial birefringent crystals such as quartz, asingle symmetry axis (actually a direction) known as the optic axisdisplays two distinct principal indices of refraction: the maximum indexn_(o) (the slow axis) and the minimum index n_(e) (the fast axis).

[0064] According to the terminology of uniaxial crystals, the followinglabels are used: fast axis and slow axis. Whichever axis has thesmallest refractive index is the fast axis. If n_(e)<n_(o), as is thecase with quartz, then the extraordinary axis is fast and the ordinaryaxes are slow. Conversely, if n_(e)>n_(o), as with calcite and MgF₂,then the extraordinary axis is slow, and the ordinary axes are fast. Bydefinition, quartz is said to be a positive uniaxial crystal, whereascalcite is a negative uniaxial crystal. These two indices correspond tolight field oscillations parallel and perpendicular to the optic axis.

[0065] Input light that is linearly polarized along the crystal'sordinary acts as an ordinary wave and will experience refractive indexno. Rotating the crystal so that the light is linearly polarized alongthe crystal's extraordinary axis causes the light to act as anextraordinary wave which sees a refractive index n_(e). In these twocases, the phase delays, or optical path length, will be different eventhough the light travels the same physical path length.

[0066] Thus for quartz, the maximum index results in ordinary rayspassing through the material along one optical path. The minimum indexresults in extraordinary rays passing through the material along anotheroptical path. The velocities of the extraordinary and ordinary raysthrough the birefringent materials vary intensely with their refractiveindices. The difference in velocities gives rise to a phase differencewhen the two beams recombine. In the case of an incident linearlypolarized beam this is given by:${\alpha = {2\pi \quad d\frac{\left( {n_{e} - n_{o}} \right)}{\lambda}}};$

[0067] where α is the phase difference; d is the thickness of waveplate; n_(e), n_(o) are the refractive indices of the extraordinary andordinary rays respectively, and λ is the wavelength. Thus, at anyspecific wavelength the phase difference is governed by the thickness ofthe wave plate.

[0068] The thickness of the quarter-wave plate is such that the phasedifference is ¼-wavelength (zero order) or some multiple of ¼ wavelength(multiple order). If the angle between the electric field vector of theincident linearly polarized beam and the retarder principal plane of thequarter-wave plate is 45 degrees, the emergent beam is circularlypolarized.

[0069] Additionally, when a quarter-wave plate is double passed, e.g.,when the light passes through it twice because it is reflected off amirror, it acts as a half-wave plate and rotates the plane ofpolarization to a certain angle.

[0070] By quarter-wave plate is meant a thickness of birefringentmaterial which introduces a quarter of a wavelength of the incidentlight. This is in contrast to an integral number of half plusquarter-waves or two thicknesses of material whose phase retardancediffers by a quarter-wave. The deleterious effects of large angle ofincidence variations are thereby minimized at the high numericalaperture by the use of such zero order wave plates, and by restrictingthe field size in the plane of incidence.

[0071] Similarly, the thickness of a half-wave plate is such that thephase difference is ½-wavelength (zero order) or some odd multiple of½-wavelength (multiple order). A linearly polarized beam incident on ahalf-wave plate emerges as a linearly polarized beam but rotated suchthat its angle to the optical axis is twice that of the incident beam.

[0072] While variable wave plates can be in several ways, thecharacteristics of these plates may have detrimental properties similarto those of multiple order discussed above. However, there aretechniques available for making zero order wave plates whose retardationcan be continuously adjusted. Such a variable wave plate is also calleda polarization compensator, and it can be used to achieve anyretardation, including quarter-wave and half-wave, for a broad range ofwavelengths. Predominantly, there are two types of compensators: theBerek's compensator and the Soleil-Babinet compensator.

[0073] The properties of there two compensators are shown in FIGS. 2Band 2C.

[0074]FIG. 2B illustrates the properties of a Berek's compensator. FIG.2C illustrates the properties of a Soleil-Babinet compensator.

[0075] The Berek's compensator 250, shown in FIG. 2B, is made from asingle plate cut with the extraordinary axis perpendicular to the plate.When light 240 is at normal incidence to the plate, it propagates with avelocity independent of polarization. There is no retardation in outputlight 245 because the light only experiences a refractive index n_(o).The light is “ignorant” of the extraordinary axis. But, when the plate250 is tilted toward or away from the light 240, as shown by plate 250′,then one of the axes in the plane of incidence becomes slightlyextraordinary. The axis now has an effective refractive index n′_(e)given by the formula:$\frac{1}{n_{e}^{\prime}} = \sqrt{\frac{\cos^{2}\theta_{R}}{n_{o}^{2}} + \frac{\sin^{2}\theta_{R}}{n_{e}^{2}}}$

[0076] The extraordinary axis is perpendicular to the plate. Tilt causesbirefringence and thus phase retardation in output light 245′. Eventhough the amount of retardation in the Berek's compensator depends onthe degree of tilt, it has angular sensitivity equal to a othercompensators. The Berek's compensator is attractive because it consistsof only one plate of uniaxial crystal, thereby cutting down on the costand optical loss while still maintaining the versatility of theSoleil-Babinet, discussed below.

[0077] The Soleil-Babinet effectively consists of two uniaxial platesstacked together. FIG. 2C shows plates 260 and 270, and 280 and 290. Theextraordinary axes of the two plates are perpendicular to each other sothe roles of the ordinary and extraordinary axes are reversed as thelight travels through one plate and then the other. A phase differenceor retardation that is accumulated in plate 260(280) may be partially orcompletely canceled out by plate 270(290).

[0078] A variable compensator is made by designing plate 260(280) as twocomplementary wedges, shown as wedge pair 263 and 265 and pair 283 and285.

[0079] In this manner, the total effective thickness of plate 260(280)can be adjusted by sliding wedge 263 with respect to wedge 265. This isillustrated in FIG. 2C. When the thickness of plate 260(280) is exactlyequal to the thickness of plate 270(290), there is zero net retardation.

[0080] Although its operation is easily understood, a Soleil-Babinetcompensator can be relatively expensive because it requires three piecesof carefully crafted and mounted uniaxial crystal. Another drawback ofthe Soleil-Babinet is that it may be quite lossy due to reflections fromthe six interfaces present in the design.

[0081] V. Example Implementations

[0082] A. Optical System With Control of Laser Illumination Polarization

[0083] The present invention uses variable wave plates to minimize doseerrors in a polarization sensitive projection optic system caused by thevariation of birefringence over the reticle. As described with respectto the figures, a single polarization compensator provides a singlecorrection for the entire reticle. In one embodiment, multiple complexcorrectors can provide a correction that varies as a function of reticleposition.

[0084] In another embodiment, the compensator system can be designed tooffset the illumination polarization to compensate for local reticlebirefringence.

[0085] In one embodiment, for dose control, the polarization state canbe evaluated over the exposure. For example, the polarization state canbe averaged over the reticle. FIG. 3 illustrates an embodiment of thepresent invention that eliminates such asymmetries or print biases. ABerek's compensator 305 is introduced before the object or reticle plane110. Berek's compensator 305 fine-tunes the light in the reticle planepolarization so that it more closely matches the desired state at thereticle plane. In one embodiment, where there is a loss free opticalillumination system, the compensator introduces a correction to thepolarization that is equal to the polarization error without thecompensator. The correction is the departure from the desired state butwith the opposite sign. If the projection optic has a small unintendedamount of birefringence before any strong polarizers, then theillumination compensator can be offset an additional amount tocompensate for this birefringence. Thus, the dose errors caused by thebirefringence of the reticle are minimized and linewidth CD controlimproved.

[0086] B. Alternate Embodiment

[0087] It is also apparent to one skilled in the relevant art that aSoleil-Babinet compensator 405 could be inserted into the system beforereticle 110 in place of Berek's compensator 305. This embodiment isshown in FIG. 4 where Soleil-Babinet compensator 405 serves the samefunction as Berek's compensator 305 and performs within the same generalcharacteristics, as discussed above.

[0088] C. Further Embodiments

[0089] The present invention can be implemented in various projectionoptic systems. For example, the present invention can be implemented incatadioptric systems as described in detail herein, as well asrefractive and reflective systems. On skilled in the relevant art, basedat least on the teachings provided herein, would recognize that theembodiments of the present invention are applicable to other reductionsystems. More detailed embodiments of the present invention as providedbelow.

[0090] Additional embodiments having variable wave plates 505, 605, 705,805, and 905 are described in detail below with respect to FIGS. 5-9.Variable wave plates 505, 605, 705, 805, and 905 are not limited tovariable wave plates and in general can be any type of variablecompensator including but not limited to, layered wave plates, opposingmirrors, Berek's compensators and/or Soleil-Babinet compensators.

[0091]FIG. 5 illustrates another embodiment of the optical reductionsystem of the present invention that includes a variable wave plate 505within the illumination system to provide compensation for reticlebirefringence. From its long conjugate end, it comprises a variable waveplate 505, an object or reticle plane 110, a first lens group LG1, afolding mirror 520, a second lens group LG2, a beamsplitter cube 530, afirst quarter-wave plate 532, a concave mirror 534, a secondquarter-wave plate 538, and a third lens group LG3. The image is formedat image or wafer plane 180. The first lens group LG1 comprises a shell512, a spaced doublet including positive lens 514 and negative lens 516,and positive lens 518. The shell 512 is an almost zero power or zeropower lens. The second lens group LG2 comprises a positive lens 522, aspaced doublet including a negative lens 524 and a positive lens 526,and negative lens 528. The third lens group LG3 comprises two positivelenses 540 and 542, which are strongly positive, shell 544, and twopositive lenses 546 and 548, which are weakly positive. The foldingmirror 520 is not essential to the operation of the present invention.However, the folding mirror permits the object and image planes to beparallel which is convenient for one intended application of the opticalsystem of the present invention, which is the manufacture ofsemiconductor devices using photolithography with a step and scansystem.

[0092] Radiation enters the system at the long conjugate end and passesthrough the first lens group LG1, is reflected by the folding mirror520, and passes through the second lens group LG2. The radiation entersthe beamsplitter cube 530 and is reflected from surface 536 passingthrough quarter-wave plate 532 and reflected by concave mirror 534. Theradiation then passes back through the quarter-wave plate 532, thebeamsplitter cube 530, the quarter-wave plate 538, lens group LG3, andis focused at the image or wafer plane 180.

[0093] Lens groups upstream of the mirror, LG1 and LG2, provide onlyenough power to image the entrance pupil at infinity to the aperturestop 531 at or near the concave mirror 534. The combined power of lensgroups LG1 and LG2 is slightly negative. The shell 512 and air spaceddoublet 514 and 516 assist in aberration corrections includingastigmatism, field curvature, and distortion. The lens group LG3, afterthe concave mirror 534, provides most of the reduction from object toimage size, as well as projecting the aperture stop to an infinite exitpupil. The two strongly positive lenses 540 and 542 provide a highnumerical aperture at the image and exit pupils and infinity. The shell544 has almost no power. The two weakly positive lenses 546 and 548 helpcorrect high order aberrations. The concave mirror 534 may provide areduction ratio of between 1.6 and 2.7 times that of the total system.

[0094] The negative lens 524 in the second lens group LG2 provides astrongly diverging beam directed at the beamsplitter cube 530 andconcave mirror 534. The strongly positive lens 522 provides lateralcolor correction. The air space doublet comprising lenses 524 and 526helps to correct spherical aberrations and coma. Concave mirror 534 ispreferably aspheric, therefore helping further reduce high orderaberrations.

[0095] The transmission losses introduced by the beamsplitter cube 530are minimized by illuminating the object or reticle with linearlypolarized light and including a quarter-wave plate 532 between thebeamsplitter cube 530 and the concave mirror 534. Additionally, byincreasing the numerical aperture in lens group LG3, after the concavemirror 534 and beamsplitter cube 530, the greatest angular range is notseen in these elements.

[0096] However, the use of linearly polarized light at numericalapertures greater than about 0.5 introduces small but noticeableasymmetries in the imaging. In the present invention, this caneffectively be removed by introducing another quarter-wave plate 538after the final passage through the beamsplitter cube 530, therebyconverting the linearly polarized light into circularly polarized light.This circularly polarized light is basically indistinguishable fromunpolarized light in its imaging behavior.

[0097] The optical system illustrated in FIG. 5 is designed to operateat a reduction ratio of 4 to 1. Therefore, the numerical aperture in theimage space is reduced from 0.7 by a factor of 4 to 0.175 at the objector reticle plane 110. In other words, the object space numericalaperture is 0.175 and the image space numerical aperture is 0.7. Uponleaving the first lens group LG1 the numerical aperture is reduced to0.12, a consequence of the positive power needed in lens group LG1 toimage the entrance pupil at infinity to the aperture stop of the systemclose to the concave mirror 534. The numerical aperture after leavingthe second lens group LG2 and entering the beamsplitter is 0.19.Therefore, the emerging numerical aperture from the second lens groupLG2, which is 0.19, is larger than the entering or object spacenumerical aperture of lens group LG1, which is 0.175. In other words,the second lens group LG2 has an emerging numerical aperture greaterthan the entering numerical aperture of the first lens group LG1. Thisis very similar to the object space numerical aperture, which is 0.175,due to the overall negative power of the second lens group LG2. This iscontrary to prior art systems where the numerical aperture entering abeamsplitter cube is typically close to zero or almost collimated. Theconcave mirror 534 being almost concentric, the numerical aperture ofthe radiation reflected from it is increased only slightly from 0.19 to0.35. The third lens group LG3 effectively doubles the numericalaperture to its final value of 0.7 at the wafer or image plane 180.

[0098] The present invention achieves its relatively high numericalaperture without obstruction by the edges of the beamsplitter cube bymeans of the negative second group LG2 and the strongly positive thirdlens group LG3. The use of the beamsplitter cube 530 rather than a platebeamsplitter is important in the present invention because at numericalapertures greater than about 0.45 a beamsplitter cube will providebetter performance. There is a reduction of the numerical aperturewithin the cube by the refractive index of the glass, as well as theabsence of aberrations that would be introduced by a tilted platebeamsplitter in the non-collimated beam entering the beamsplitter. Theconstruction data for the lens system illustrated in FIG. 5 according tothe present invention is given in Table 1 below. TABLE 1 Radius ofAperture Element Curvature (mm) Thickness Diameter (mm) Number FrontBack (mm) Front Back Glass 505 Infinite Infinite 33.1000 123.0000123.0000 Quartz Space 0.7500 110 Infinite 63.3853 Space 0.7500 512−158.7745 −177.8880 15.0000 124.0478 131.7725 Silica Space 36.1130 514−556.6911 −202.0072 22.2126 148.3881 152.5669 Silica Space 38.7188 516−183.7199 −558.8803 15.0000 156.5546 166.5750 Silica Space 10.0674 518427.2527 −612.2450 28.8010 177.4010 179.0292 Silica Space 132.3320 520Infinite −74.0000 184.6402 Reflection 522 −240.4810 2050.9592 −33.3135188.4055 185.3395 Silica Space −29.3434 524 421.7829 −145.6176 −12.0000175.5823 169.0234 Silica Space −4.2326 526 −150.4759 472.0653 −46.5091171.4244 169.9587 Silica Space −2.0000 528 −1472.2790 −138.2223 −15.0000165.3586 154.8084 Silica Space −27.2060 530 Infinite Infinite −91.8186155.6662 253.0917 Silica 536 Infinite 253.0917 Reflection 530 InfiniteInfinite 91.8186 253.0917 253.0917 Silica Space 2.0000 532 InfiniteInfinite 6.0000 185.8693 186.8401 Silica Space 17.9918 Stop 188.0655 534Aspheric −17.9918 188.0655 Reflection 532 Infinite Infinite −6.0000183.5471 180.1419 Silica Space −2.0000 530 Infinite Infinite −91.8186178.3346 149.2832 Silica 530 Infinite Infinite −70.000 149.2832 128.8604Silica Space −2.0000 538 Infinite Infinite −4.500 127.9681 126.6552Silica Space −0.7500 540 −175.1330 1737.4442 −17.7754 121.4715 118.2689Silica Space −0.7500 542 −108.8178 −580.1370 −18.2407 104.5228 97.7967Silica Space −0.7500 544 −202.2637 −86.6025 −31.1216 91.7061 57.4968Silica Space −2.3507 546 −122.1235 −488.7122 −17.9476 56.4818 41.1675Silica Space −0.2000 548 −160.8506 −360.1907 −6.1500 39.4528 33.5764Silica Space −4.000 180 Infinite 26.5019

[0099] Concave mirror 534 has an aspheric reflective surface accordingto the following equation: $\begin{matrix}{Z = \quad {\frac{({CURV})Y^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)({CURV})^{2}Y^{2}}}} + {(A)Y^{4}} +}} \\{\quad {{{(B)Y^{6}} + {(D)Y^{10}} + {(E)Y^{12}} + {(F)Y^{14}}};}}\end{matrix}$

[0100] wherein the constants are as follows:

[0101] CURV=−0.00289051

[0102] K=0.000000

[0103] A=6.08975×10⁻¹¹

[0104] B=2.64378×10¹⁴

[0105] C=9.82237×10⁻¹⁹

[0106] D=7.98056×10⁻²³

[0107] E=−5.96805×10⁻²⁷

[0108] F=4.85179×10⁻³¹

[0109] The lens according to the construction in Table 1 is optimizedfor radiation centered on 248.4 nanometers. The single refractingmaterial of fused silica and the large portion of refracting powerrestricts the spectral bandwidth of the embodiment illustrated in FIG. 5to about 10 picometers or 0.01 nanometers. This spectral bandwidth ismore than adequate for a line narrowed krypton fluoride excimer laserlight source. The embodiment illustrated in FIG. 5 can be optimized forany wavelength for which fused silica transmits adequately.

[0110] A wider spectral bandwidth can be achieved by the use of twooptical materials with different dispersions. A second embodiment of thepresent invention is illustrated in FIG. 6. From its long conjugate end,it comprises a first quarter-wave plate 608, an object or reticle plane110, a second quarter-wave plate 611, a lens group LG4, a folding mirror622, a lens group LG5, a beamsplitter cube 632 having surface 638, afirst quarter-wave plate 634, a concave mirror 636, a secondquarter-wave plate 640, and lens group LG6. The image is formed at imageor wafer plane 180. The lens group LG4 comprises a spaced doubletincluding negative lens 612 and positive lens 614, a weak positive lens616, positive lens 618, and shell 620. The lens group LG5 comprises apositive lens 624, a negative lens 626, a positive lens 628, and anegative lens 630. The lens group LG6 comprises two positive lenses 642,cemented doublet including positive lens 644 and negative lens 646,positive lens 648, and cemented doublet including shell 650 and positivelens 652.

[0111] This second embodiment uses calcium fluoride in one of theindividual positive lenses of the lens group LG4, negative lenses of thelens group LG5, and two of the positive lenses of the lens group LG6.The construction data of the second embodiment illustrated in FIG. 6 ofthe present invention is given in Table 2 below. TABLE 2 Radius ofAperture Element Curvature (mm) Thickness Diameter (mm) Number FrontBack (mm) Front Back Glass 605 Infinite Infinite 33.1000 123.0000123.0000 Quartz Space 0.5000 110 Infinite 60.4852 Space 0.5000 612−205.5158 539.1791 15.2158 124.0926 137.3346 Silica Space 8.8054 6142080.9700 −210.6539 32.4984 142.6149 151.7878 Silica Space 1.2676 616310.4463 700.3748 40.7304 162.4908 165.2126 CaFl Space 0.5000 618634.1820 −798.8523 27.5892 165.4595 166.4747 Silica Space 0.5000 6201480.0597 1312.1247 25.4322 168.7516 164.7651 Silica Space 136.2343 622Infinite −74.0000 161.9590 Reflection 624 −761.9176 1088.9351 −19.2150160.3165 159.2384 Silica Space −19.9465 626 648.8361 −202.5872 −12.0000155.1711 153.0635 CaFl Space −7.6304 628 −400.4276 458.5060 −25.8769153.0635 153.8055 Silica Space −2.0000 630 −818.0922 −168.5034 −27.5927152.6663 147.5200 CaFl Space −20.5014 632 Infinite Infinite −91.7553148.6158 252.7349 Silica 638 Infinite 252.7349 Reflection 632 InfiniteInfinite 91.7553 252.7349 252.7349 Silica Space 2.0000 634 InfiniteInfinite 6.0000 185.8070 187.0026 Silica Space 18.1636 Stop 188.5681 636Aspheric −18.1636 188.5681 Reflection 634 Infinite Infinite −6.0000184.2566 181.1084 Silica Space −2.0000 632 Infinite Infinite −91.7553179.3838 151.7747 Silica 632 Infinite Infinite −70.0000 151.7747133.3985 Silica Space −2.0000 640 Infinite Infinite −4.5000 132.5690131.3876 Silica Space −0.5000 642 −112.0665 −597.6805 −21.4866 123.4895119.2442 Silica Space −0.5000 644 −116.3137 282.3140 −24.0940 107.8451101.2412 CaFl 646 282.3140 −66.5293 −13.7306 101.2412 72.6862 SilicaSpace −2.6346 648 −77.2627 −374.4800 −17.9594 72.0749 62.7659 SilicaSpace −0.5452 650 −130.1381 −57.1295 −20.8147 58.9696 37.4889 Silica 652−57.1295 −7305.8777 −6.1425 37.4889 34.3156 CaFl Space −4.0000 180Infinite 26.4992

[0112] wherein the constants for the aspheric mirror 634 used in theequation after Table 1 are as follows:

[0113] CURV=−0.00286744

[0114] K=0.000000

[0115] A=−1.92013×10⁻⁰⁹

[0116] B=−3.50840×10 ⁻¹⁴

[0117] C=2.95934×10⁻¹⁹

[0118] D=−1.10495×10 ⁻²²

[0119] E=9.03439×10⁻²⁷

[0120] F=−1.39494×10⁻³¹

[0121] This second embodiment is optimized for radiation centered on193.3 nanometers and has a spectral bandwidth of about 200 picometers or0.2 nanometers. A slightly line narrowed argon fluoride excimer laser isan adequate light source. Additionally, the design can be optimized forany wavelength for which both refractive materials transmit adequately.The bandwidth will generally increase for longer wavelengths, as thematerial dispersions decrease. For example, around 248.4 nanometers sucha two-material design will operate over at least a 400 picometers, 0.4nanometers bandwidth.

[0122] At wavelengths longer than 360 nanometers, a wider range ofoptical glasses begin to have adequate transmission. A third embodimentillustrated in FIG. 7 takes advantage of this wider selection of glassesand further reduced dispersion. From its long conjugate end, itcomprises an object or reticle plane 110, a lens group LG7, a foldingmirror 722, a lens group LG8, a beamsplitter cube 732 having a surface738, a first quarter-wave plate 734, a concave mirror 736, a secondquarter-wave plate 740, and lens group LG9. The image is formed at imageor wafer plane 180. The lens group LG7 comprises a spaced doubletcomprising negative lens 712 and positive lens 714, spaced doubletincluding positive lens 716 and negative lens 718, and positive lens720. The lens group LG8 comprises a positive lens 724, a negative lens726, a positive lens 728, and a negative lens 730. The lens group LG9comprises a positive lenses 742, cemented doublet including positivelens 744 and negative lens 746, positive lens 748, and cemented doubletincluding shell 750 and positive lens 752.

[0123] The construction data of the third embodiment illustrated in FIG.7 is given in Table 3 below. TABLE 3 Radius of Aperture ElementCurvature (mm) Thickness Diameter (mm) Number Front Back (mm) Front BackGlass 705 Infinite Infinite 33.1000 123.0000 123.0000 Quartz Space0.5000 110 Infinite 59.2960 Space 0.5000 712 −620.7809 361.8305 20.2974125.9406 134.7227 PBM2Y Space 2.6174 714 515.7935 −455.1015 39.8858135.3384 145.6015 PBM2Y Space 14.7197 716 431.3189 −239.4002 36.9329155.6269 157.3014 BSL7Y Space 0.5000 718 −259.6013 685.3286 26.3534156.9363 162.2451 PBM2Y Space 1.4303 720 361.5709 −1853.2955 23.3934168.7516 165.1801 BAL15Y Space 131.8538 722 Infinite −77.8469 169.9390Reflection 724 −429.2950 455.4247 −32.3086 173.0235 171.1102 PBL6Y Space−27.6206 726 401.0363 −180.0031 −12.0000 159.3555 154.7155 BSL7Y Space−5.6227 728 −258.4722 1301.3764 −26.1321 154.7155 154.1517 PBM8Y Space−2.0000 730 −1282.8931 −180.2226 −12.0000 153.1461 149.4794 BSL7Y Space−19.7282 732 Infinite Infinite −91.7349 150.4585 252.6772 Silica 738Infinite 252.6772 Reflection 732 Infinite Infinite 91.7349 252.6772252.6772 Silica Space 2.0000 734 Infinite Infinite 6.0000 185.6435186.7758 Silica Space 18.2715 Stop 188.1745 736 Aspheric −18.2715188.1745 Reflection 734 Infinite Infinite −6.0000 183.6393 180.1377Silica Space −2.0000 732 Infinite Infinite −91.7349 178.3236 147.9888Silica 732 Infinite Infinite −70.0000 147.9888 126.9282 Silica Space−2.000 740 Infinite Infinite −4.5000 126.0289 124.6750 Silica Space−0.5000 742 −119.8912 −610.6840 −18.6508 117.5305 113.4233 BSM51Y Space−0.5000 744 −114.1327 384.9135 −21.1139 102.6172 96.4137 BSL7Y 746384.9135 −70.2077 −13.0576 96.4137 71.1691 PBL26Y Space −2.8552 748−85.7858 −400.3240 −16.9147 70.5182 61.2633 BSM51Y Space −0.8180 750−151.5235 −54.0114 −19.5810 57.6234 37.3909 BSM51Y 752 −54.0114−2011.1057 −6.3947 37.3909 34.2119 PBL6Y Space −4.0000 180 Infinite26.5002

[0124] wherein the constants for the aspheric mirror 736 used in theequation after Table 1 as follows:

[0125] CURV=−0.00291648

[0126] K=0.000000

[0127] A=−1.27285×10⁻⁹

[0128] B=−1.92865×10⁻¹⁴

[0129] C=6.21813×10⁻¹⁹

[0130] D=−6.80975×10²³

[0131] E=6.04233×10⁻²⁷

[0132] F=3.64479×10⁻³²

[0133] This third embodiment operates over a spectral bandwidth of 8nanometers centered on 365.5 nanometers. A radiation of this spectralbandwidth can be provided by a filtered mercury arc lamp at the I-linewaveband. The optical glasses other than fused silica used in this thirdembodiment are commonly known as I-line glasses. These optical glasseshave the least absorption or solarization effects at the mercury I-linewavelength.

[0134]FIG. 8 illustrates a fourth embodiment of the optical reductionsystem of the present invention. This embodiment has a numericalaperture of 0.63 and can operate at a spectral bandwidth of 300picometers, and preferably of 100 picometers, centered on 248.4nanometers. From the long conjugate end, it includes an object orreticle plane 110, a first lens group LG1, a folding mirror 820, asecond lens group LG2, a beamsplitter cube 830, a first quarter-waveplate 832, a concave mirror 834, a second quarter-wave plate 838, and athird lens group LG3. The image is formed at the image or wafer plane180.

[0135] The first lens group LG1 comprises a shell 812, a spaced doubletincluding a positive lens 814 and a negative lens 816, and a positivelens 818. The second lens group LG2 comprises a positive lens 822, aspaced doublet including a negative lens 824 and a positive lens 826,and a negative lens 828. The third lens group LG3 comprises two positivelenses 840 and 842, a shell 844, and two positive lenses 846 and 848.Again, as in the embodiment illustrated in FIG. 5, the folding mirror820 of FIG. 8 is not essential to the operation of the invention, butnevertheless permits the object 110 and image plane 180 to be parallelto each other which is convenient for the manufacture of semiconductordevices using photolithography.

[0136] The construction data of the fourth embodiment illustrated inFIG. 8 is given in Table 4 below. TABLE 4 Radius of Aperture ElementCurvature (mm) Thickness Diameter (mm) Number Front Back (mm) Front BackGlass 805 Infinite Infinite 33.1000 123.0000 123.0000 Quartz Space2.0000 110 Infinite 63.3853 Space 2.0000 812 −183 5661   −215 7867CX17.0000 122.8436 130.6579 Silica Space 46.6205 814 −601.1535CC −2309702CX 21.4839 149.1476 153.3103 Silica Space 68.8075 816 −191.1255 −3454510CX 15.0000 161.6789 170.1025 Silica Space 3.0000 818   435 8058CX−1045 1785CX  24.9351 177.4250 178.2672 Silica Space 130.0000Decenter(1) 820 Infinite −64.5000 180.3457 Reflection 822 −210.7910CX380.1625CX −43.1418 181.6672 178.0170 Silica Space −15.8065 824   3001724CC −123.4555CC −12.0000 166.7278 152.3101 Silica Space −3.8871 826−126.8915CX   972 6391CX −41.3263 154.8530 151.8327 Silica Space −1.5000828 −626.4905CX −116.6456CC −12.0000 147.6711 136.1163 Silica Space−31.8384 830 Infinite Infinite −74.0000 137.2448 200.1127 SilicaDecenter(2)| 836 Infinite 200.1128 Reflection 830 Infinite Infinite74,0000 200.1127 200.1127 Silica Space 2.0000 832 Infinite Infinite6.0000 148.6188 149.0707 Silica Space 14.4638 Stop 149.6392 834 Aspheric−14.4638 149.6392 Reflection 832 Infinite Infinite −6.0000 144.8563141.2737 Silica Space −2.0000 830 Infinite Infinite −74.000 139.3606117.3979 Silica Decenter(3) 830 Infinite Infinite −61.000 117.3979100.5074 Silica Space −2.0000 838 Infinite Infinite −4.5000 99.661798.4157 Silica Space −1.2000 840 −157.8776CX 2282.2178CX −13.750194.8267 91.8775 Silica Space −1.2000 842    −94 0059CX  −46 6659CC−13.4850 82.8663 78.1418 Silica Space −1.2000 844 −147.2485CX −77.8924CC−22.2075 72.7262 50.6555 Silica Space −3.2091 846 −159.2880CX−519.4850CC −13.8321 49.5648 39.0473 Silica Space −0.2000 848 −1293683CX −426.7350CC −6.1500 37.3816 32.4880 Silica Space Image Distance =−4.0000 850 Image Infinite

[0137] The constants for the aspheric mirror 834 used in the equationlocated after Table 1 are as follows:

[0138] CURV=−0.00332614

[0139] K=0.000000

[0140] A=−4.32261E−10

[0141] B=3.50228E−14

[0142] C=7.13264E−19

[0143] D=2.73587E−22

[0144] This fourth embodiment is optimized for radiation centered on248.4 nm. The single refracting material of fused silica and the largeportion of refracting power restricts the spectral bandwidth of theembodiment depicted in FIG. 8. However, because the fourth embodimenthas a maximum numerical aperture of 0.63 rather than of 0.7 as in thefirst three embodiments, the fourth embodiment provides acceptableimaging over a spectral full-width-half-maximum bandwidth of 300picometers, or preferably of 100 picometers. Thus, in the former, anunnarrowed, or, in the latter, a narrowed excimer laser can be employedfor the illumination source.

[0145] The fourth embodiment differs from the first three embodiments inthat the net power of LG1 and LG2 of the fourth embodiment is weaklypositive rather than weakly negative as in the first three embodiments.In addition, this illustrates that the overall focal power of LG1 plusLG2 can be either positive or negative and still permit an infinitelydistant entrance pupil to be imaged at or near the concave mirror 834.

[0146]FIG. 9 illustrates a fifth embodiment of the optical reductionsystem of the present invention. Preferably, this embodiment has anumerical aperture of 0.60 and operates at a spectral bandwidth of 300picometers centered on 248.4 nanometers. From the long conjugate end, itincludes a variable wave plate 905 within the illumination system, anobject or reticle plane 110, a first lens group LG1, a folding mirror920, a second lens group LG2, a beamsplitter cube 930, a firstquarter-wave plate 932, a concave mirror 934, a second quarter-waveplate 938, and a third lens group LG3. The image is formed at an imageor wafer plane 180.

[0147] The first lens group LG1 comprises a shell 912, a spaced doubletincluding a positive lens 914 and a negative lens 916, and a positivelens 918. The second lens group LG2 comprises a positive lens 922, aspaced doublet including a negative lens 924 and a positive lens 926,and a negative lens 928. The third lens group LG3 comprises two positivelenses 940 and 942, a shell 944, and two positive lenses 946 and 948.Again, as in the embodiment illustrated in FIG. 5, the folding mirror920 of FIG. 9 is not essential to the operation of the invention, butnevertheless permits the object and image planes to be parallel to eachother which is convenient for the manufacture of semiconductor devicesusing photolithography.

[0148] The construction data of the fifth embodiment illustrated in FIG.9 is in Table 5 below. TABLE 5 Radius of Aperture Element Curvature (mm)Thickness Diameter (mm) Number Front Back (mm) Front Back Glass 905Infinite Infinite 33.1000 123.0000 123.0000 Quartz Space 1.1880 910Infinite 62.7514 Space 1.1880 912 −136 1154CC −152.5295CX 16.8300120.7552 129.4354 Silica Space 4.5206 914 −270 1396CC −191 8742CX20.5341 132.9152 139.0377 Silica Space 90.8476 916 −188.9000CC −2847476CX 17.5000 156.1938 165.6567 Silica Space 2.9700 918 433 8174CX −8415599CX 25.8293 173.8279 174.8334 Silica Space 149.4549 Decenter( 1) 920Infinite −61.0000 177.2183 Reflection 922 −190 3251CX −8413 4836CC −34.4584 178.5071 174.2260 Silica Space −51.5487 924   690 5706CC −1464997CC −11.8800 150.4109 141.8021 Silica Space −10.6267 526 −265 9886CX1773 5314CX −24.1851 142.1851 141.2400 Silica Space −1.5000 928 −2449899CX −142 8558CC −11.8800 139.3290 133.8967 Silica Space −21.6411 930Infinite Infinite −71.2800 134.3115 189.7826 Silica Decenter(2) 936Infinite 189.7826 Reflection 930 Infinite Infinite 71.2800 189.7826189.7826 Silica Space 1.9800 932 Infinite Infinite 5.9400 142.3429142.6707 Silica Space 18.5263 Stop 143.5034 934 Aspheric −18.5263143.5034 Reflection 932 Infinite Infinite −5.9400 134.2788 130.9398Silica Space −1.9800 930 Infinite Infinite −71.2800 130.1221 111.7247Silica Decenter (3) 930 Infinite Infinite −60.4000 111.7247 96.1353Silica Space −1.9800 938 Infinite Infinite −4.4550 95.3562 94.2064Silica Space −1.1880 940 −127 4561CX −1398 8019CC −13.0104 90.473787.7002 Silica Space −1.1880 942 −98.8795CX −424.1302CC −12.2874 80.701676.3270 Silica Space −1.1880 944 −132 0104CX −70.9574CC −17.8706 71.078953.4306 Silica Space −3.1246 946 −123.1071CX −585.4471CC −19.949652.6417 38.2256 Silica Space −0.1980 948 −137.8349CX −292.6179CX −6.088536.7251 31.8484 Silica Space Image Distance = −4.0000 950 Image Infinite26.5000

[0149] The constants for the aspheric mirror 934 used in the equationlocated after Table 1 are as follows:

[0150] CURV=−0.00325995

[0151] K=0.000000

[0152] A=−6.91799E−10

[0153] B=5.26952E−15

[0154] C=6.10046E−19

[0155] D=1.59429E−22

[0156] This fifth embodiment is optimized for radiation centered on248.4 mn. The single refracting material of fused silica and the largeportion of refracting power restricts the spectral bandwidth of theembodiment depicted in FIG. 9. However, because the fifth embodiment hasa maximum numerical aperture of 0.6 rather than of 0.7 as in the firstthree embodiments, the fifth embodiment provides acceptable imaging overa spectral full-width-half-maximum bandwidth of 300 picometers. Thus, anunnarrowed excimer laser can be employed for an illumination source. Thefifth embodiment differs from the first three embodiments in that thenet power of LG1 and LG2 of the fifth embodiment is weakly positiverather than weakly negative as in the first three embodiments. Inaddition, this illustrates that the overall focal power of LG1 plus LG2can be either positive or negative and still permit an infinitelydistant entrance pupil to be imaged at or near the concave mirror 934.

CONCLUSION

[0157] While specific embodiments of the present invention have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. It will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined in the appended claims. Thus, the breadth and scopeof the present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

What is claimed is:
 1. In a photolithographic tool, an optical reductionsystem having an object space numerical aperture comprising: apolarization compensator that provides a variable wavelengthpolarization difference; and an object that transmits a projected image,wherein said polarization difference of said polarization compensatorprovides alters the light projected from said object.
 2. The opticalreduction system of claim 1, further comprising: a first lens having anegative power with an emerging numerical aperture, said emergingnumerical aperture being larger than the object space numericalaperture; a beamsplitter that separates light incident from said firstlens; a concave mirror; and a second lens having a positive power,wherein said polarization compensator alters the polarization of thelight received by said first lens, the negative power of said first lensprovides enough power to image an entrance pupil of the system atinfinity to an aperture stop at or near said mirror, and the positivepower of said second lens provides substantially all of the power of thesystem and images the exit pupil of the system to infinity.
 3. Anoptical reduction system from the long conjugate end to the shortconjugate end, comprising: a variable wave plate; a reticle, whereinsaid variable wave plate provides elliptically polarized light, and saidreticle provides linearly polarized light; a first lens group ofpositive power, said first lens group having an entering numericalaperture; a second lens group of negative power, said second lens groupseparated from said first lens group and having an emerging numericalaperture greater than the entering numerical aperture of said first lensgroup; a beamsplitter; a quarter-wave plate; a concave mirror; a thirdlens group of positive power; and wherein the positive power of saidfirst lens group provides enough power to image an entrance pupil of thesystem at infinity through said second lens group to an aperture stop ator near said mirror, the negative power of said second lens groupprovides the necessary conjugates for said concave mirror, and thepositive power of said third lens group provides the remainder of thetotal system power and images the exit pupil of the system to infinity.4. The optical reduction system as in claim 3 further comprising: saidvariable wave plate is a Berek's compensator.
 5. The optical reductionsystem as in claim 3 wherein: said variable wave plate is aSoleil-Babinet compensator.
 6. The optical reduction system as in claim4 further comprising: a first quarter-wave plate placed between saidbeamsplitter and said concave mirror.
 7. The optical reduction system asin claim 6 further comprising: a second quarter-wave plate placedbetween said beamsplitter and said third lens group.
 8. An opticalreduction system from the long conjugate end to the short conjugate end,comprising: a variable wave plate; a reticle; a first lens group ofpositive power; a second lens group of negative power; a beamsplitter; afirst quarter-wave plate; a concave mirror; a third lens group ofpositive power; said first lens group including, at least one lens ofpositive power; a first lens of substantially zero power; and a firstdoublet, whereby said first lens of substantially zero power and saidfirst doublet help correct aberrations such as astigmatism, fieldcurvature, and distortion, said second lens group including, at leastone lens of negative power; a positive lens; and a second doublet,whereby said at least one lens of negative power provides a divergingbeam for said beamsplitter and said mirror, said positive lens provideslateral color correction, and said second doublet helps to correct forspherical aberration and coma, and wherein the positive power of saidfirst lens group provides enough power to image the entrance pupil ofthe system at infinity through said second lens group to an aperturestop at or near said mirror, the negative power of said second lensgroup provides the necessary conjugates for said concave mirror, and thepositive power of said third lens group provides the remainder of thetotal system power and images the exit pupil of the system to infinity.9. The optical reduction system as in claim 8 further comprising: asecond quarter-wave plate placed between said beamsplitter and saidthird lens group.
 10. The optical reduction system as in claim 9 havinga construction according to the following data TABLE 1 Radius ofAperture Element Curvature (mm) Thickness Diameter (mm) Number FrontBack (mm) Front Back Glass variable Infinite Infinite 33.1000 123.0000123.0000 Quartz wave plate reticle Infinite 63.3853 lens in −158.7745−177.8880 15.0000 124.0478 131.7725 Silica first lens group lens in−556.6911 −202.0072 22.2126 148.3881 152.5669 Silica first lens grouplens in −183.7199 −558.8803 15.0000 156.5546 166.5750 Silica first lensgroup lens in 427.2527 −612.2450 28.8010 177.4010 179.0292 Silica firstlens group lens in −240.4810 2050.9592 −33.3135 188.4055 185.3395 Silicasecond lens group lens in 421.7829 −145.6176 −12.0000 175.5823 169.0234Silica second lens group lens in −150.4759 472.0653 −46.5091 171.4244169.9587 Silica second lens group lens in −1472.2790 −138.2223 −15.0000165.3586 154.8084 Silica second lens group beamspli Infinite Infinite−91.8186 155.6662 253.0917 Silica tter beamspli Infinite 253.0917Reflection tter beamspli Infinite Infinite 91.8186 253.0917 253.0917Silica tter first Infinite Infinite 6.0000 185.8693 186.8401 Silicaquarter- wave plate concave Aspheric −17.9918 188.0655 Reflection minorfirst Infinite Infinite −6.0000 183.5471 180.1419 Silica quarter- waveplate beamspli Infinite Infinite −91.8186 178.3346 149.2832 Silica tterbeamspli Infinite Infinite −70.000 149.2832 128.8604 Silica tter secondInfinite Infinite −4.500 127.9681 126.6552 Silica quarter- wave platelens in −175.1330 1737.4442 −17.7754 121.4715 118.2689 Silica third lensgroup lens in −108.8178 −580.1370 −18.2407 104.5228 97.7967 Silica thirdlens group lens in −202.2637 −86.6025 −31.1216 91.7061 57.4968 Silicathird lens group lens in −122.1235 −488.7122 −17.9476 56.4818 41.1675Silica third lens group 548 lens −160.8506 −360.1907 −6.1500 39.452833.5764 Silica in third lens group wafer Infinite 26.5019


11. An optical reduction system having a relatively high numericalaperture, from the long conjugate end to the short conjugate end,comprising: a variable wave plate; an object plane; a first doublet; afirst positive lens; a second positive lens; a shell; a third positivelens; a first negative lens; a forth positive lens; a second negativelens; a beamsplitter cube; a first quarter-wave plate; a concave mirror;a second quarter-wave plate; a fifth positive lens; a second doublet; asixth positive lens; and a third doublet, arranged such that radiationentering the system passes through said variable wave plate, said objectplane, said first doublet, said first positive lens, said secondpositive lens, said shell, said folding mirror, said third positivelens, said first negative lens, said second negative lens; saidbeamsplitter cube, said first quarter-wave plate, and is reflected bysaid concave mirror back through said first quarter-wave plate and saidbeamsplitter cube, and through said second quarter-wave plate, saidfifth positive lens, said second doublet; said sixth positive lens, andsaid third doublet.
 12. The optical reduction system as in claim 11wherein: said variable wave plate is a Berek's compensator.
 13. Theoptical reduction system as in claim 11 wherein: said variable waveplate is a Soleil-Babinet compensator.
 14. The optical reduction systemas in claim 13 having a construction according to the following dataTABLE 2 Radius of Aperture Element Curvature (mm) Thickness Diameter(mm) Number Front Back (mm) Front Back Glass variable Infinite Infinite33.1000 123.0000 123.0000 Quartz wave plate reticle Infinite 60.4852lens of −205.5158 539.1791 15.2158 124.0926 137.3346 Silica firstdoublet lens of 2080.9700 −210.6539 32.4984 142.6149 151.7878 Silicafirst doublet first 310.4463 700.3748 40.7304 162.4908 165.2126 CaFlpositive lens second 634.1820 −798.8523 27.5892 165.4595 166.4747 Silicapositive lens shell 1480.0597 1312.1247 25.4322 168.7516 164.7651 Silicathird −761.9176 1088.9351 −19.2150 160.3165 159.2384 Silica positivelens first 648.8361 −202.5872 −12.0000 155.1711 153.0635 CaFl negativelens forth −400.4276 458.5060 −25.8769 153.0635 153.8055 Silica positivelens second −818.0922 −168.5034 −27.5927 152.6663 147.5200 CaFl negativelens beamspli Infinite Infinite −91.7553 148.6158 252.7349 Silica ttercube beamspli Infinite 252.7349 Reflection tter cube beamspli InfiniteInfinite 91.7553 252.7349 252.7349 Silica tter cube first InfiniteInfinite 6.0000 185.8070 187.0026 Silica quarter- wave plate concaveAspheric −18.1636 188.5681 Reflection mirror first Infinite Infinite−6.0000 184.2566 181.1084 Silica quarter- wave plate beamspli InfiniteInfinite −91.7553 179.3838 151.7747 Silica tter cube beamspli InfiniteInfinite −70.0000 151.7747 133.3985 Silica tter cube second InfiniteInfinite −4.5000 132.5690 131.3876 Silica quarter- wave plate fifth−112.0665 −597.6805 −21.4866 123.4895 119.2442 Silica positive lens lensof −116.3137 282.3140 −24.0940 107.8451 101.2412 CaFl second doubletlens of 282.3140 −66.5293 −13.7306 101.2412 72.6862 Silica seconddoublet sixth −77.2627 −374.4800 −17.9594 72.0749 62.7659 Silicapositive lens lens of −130.1381 −57.1295 −20.8147 58.9696 37.4889 Silicathird doublet lens of −57.1295 −7305.8777 −6.1425 37.4889 34.3156 CaFlthird doublet wafer Infinite 26.4992


15. An optical reduction system having a relatively high numericalaperture, from the long conjugate end to the short conjugate end,comprising: a variable wave plate; an object plane; a first doublet; asecond doublet; a first positive lens; a second positive lens; a firstnegative lens; a third positive lens; a second negative lens; abeamsplitter cube; a first quarter-wave plate; a concave mirror; asecond quarter-wave plate; a fourth positive lens; a third doublet; afifth positive lens; a shell; and a sixth positive lens, arranged suchthat radiation entering the system passes through said variablewaveplate, said object plane, said first doublet, said second doublet,said first positive lens, said folding mirror, said second positivelens, said first negative lens, said third positive lens, said secondnegative lens, said beamsplitter cube, said first quarter-wave plate,and is reflected by said concave mirror back through said firstquarter-wave plate and said beamsplitter cube, and through said secondquarter-wave plate, said fourth positive lens, said third doublet, saidfifth positive lens, said shell, and said sixth positive lens.
 16. Theoptical reduction system as in claim 15 wherein: said variable waveplate is a Berek's compensator.
 17. The optical reduction system as inclaim 15 wherein: said variable wave plate is a Soleil-Babinetcompensator.
 18. The optical reduction system as in claim 17 having aconstruction according to the following data TABLE 3 Radius of ApertureElement Curvature (mm) Thickness Diameter (mm) Number Front Back (mm)Front Back Glass variable Infinite Infinite 33.1000 123.0000 123.0000Quartz wave plate reticle Infinite 59.2960 lens of −620.7809 361.830520.2974 125.9406 134.7227 PBM2Y first doublet lens of 515.7935 −455.101539.8858 135.3384 145.6015 PBM2Y first doublet lens of 431.3189 −239.400236.9329 155.6269 157.3014 BSL7Y second doublet lens of −259.6013685.3286 26.3534 156.9363 162.2451 PBM2Y second doublet first 361.5709−1853.2955 23.3934 168.7516 165.1801 BAL15Y positive lens second−429.2950 455.4247 −32.3086 173.0235 171.1102 PBL6Y positive lens first401.0363 −180.0031 −12.0000 159.3555 154.7155 BSL7Y negative lens third−258.4722 1301.3764 −26.1321 154.7155 154.1517 PBM8Y positive lenssecond −1282.8931 −180.2226 −12.0000 153.1461 149.4794 BSL7Y negativelens beamspli Infinite Infinite −91.7349 150.4585 252.6772 Silica ttercube beamspli Infinite 252.6772 Reflection tter cube beamspli InfiniteInfinite 91.7349 252.6772 252.6772 Silica tter cube first InfiniteInfinite 6.0000 185.6435 186.7758 Silica quarter- wave plate concaveAspheric −18.2715 188.1745 Reflection mirror first Infinite Infinite−6.0000 183.6393 180.1377 Silica quarter- wave plate beamspli InfiniteInfinite −91.7349 178.3236 147.9888 Silica tter cube beamspli InfiniteInfinite −70.0000 147.9888 126.9282 Silica tter cube second InfiniteInfinite −4.5000 126.0289 124.6750 Silica quarter- wave plate fourth−119.8912 −610.6840 −18.6508 117.5305 113.4233 BSM51Y positive lens lensof −114.1327 384.9135 −21.1139 102.6172 96.4137 BSL7Y third doublet lensof 384.9135 −70.2077 −13.0576 96.4137 71.1691 PBL26Y third doublet fifth−85.7858 −400.3240 −16.9147 70.5182 61.2633 BSM51Y positive lens shell−151.5235 −54.0114 −19.5810 57.6234 37.3909 BSM51Y sixth −54.0114−2011.1057 −6.3947 37.3909 34.2119 PBL6Y positive lens wafer Infinite26.5002


19. An optical reduction system having a relatively high numericalaperture, from the long conjugate end to the short conjugate end,comprising: an object plane; a first lens group of positive power; asecond lens group of negative power; a beamsplitter; a concave mirror; athird lens group of positive power; a variable wave plate placed beforesaid object plane; a first quarter-wave plate placed between saidbeamsplitter and said concave mirror; a second quarter-wave plate placedbetween said beamsplitter and said third lens group; and wherein theproperties of said variable wave plate elliptically polarize thelinearly polarized radiation entering the system, and the properties ofsaid object plane linearly polarize the elliptically polarized radiationleaving said object plane.
 20. The optical reduction system as in claim19 wherein: said variable wave plate is a Berek's compensator.
 21. Theoptical reduction system as in claim 19 wherein: said variable waveplate is a Soleil-Babinet compensator.
 22. An optical reduction systemhaving a relatively high numerical aperture, from the long conjugate endto the short conjugate end, comprising: a variable wave plate; an objectplane; a first lens group of positive power; a second lens group ofnegative power, said first and second lens group having a net power; abeamsplitter, the net power of said first and second lens groupresulting in a non-collimated beam entering said beamsplitter from saidfirst and second lens group; a first quarter-wave plate; a concavemirror, the net power of said first and second lens group providing onlyenough power to image the system entrance pupil at infinity to anaperture stop at or near said concave mirror; a second quarter-waveplate; and a third lens group of positive power; arranged such thatradiation entering said system passes through said first lens group,said second lens group, said beamsplitter, and is reflected by saidconcave mirror back through said beamsplitter and through said thirdlens group.
 23. The optical reduction system as in claim 22 wherein:said variable wave plate is oriented with the input light such that theproperties of said variable wave plate elliptically polarize thelinearly polarized light, and the properties of said object planelinearly polarize the elliptically polarized radiation leaving saidobject plane.
 24. The optical reduction system as in claim 23 having aconstruction according to the following data TABLE 4 Radius of ApertureElement Curvature (mm) Thickness Diameter (mm) Number Front Back (mm)Front Back Glass variable Infinite Infinite 33.1000 123.0000 123.0000Quartz wave plate reticle Infinite 63.3853 lens of −183.5661 −215.7867CX17.0000 122.8436 130.6579 Silica first lens group lens of −601.1535CC−230.9702CX 21.4839 149.1476 153.3103 Silica first lens group lens of−195.1255 −345.4510CX 15.0000 161.6789 170.1025 Silica first lens grouplens of 435.8058CX − −24.9351 177.4250 178.2672 Silica first lens1045.1785C group X lens of −210.7910CX 380.1625CX −43.1418 181.6672178.0170 Silica second lens group lens of 300.1724CC −123.4555CC−12.0000 166.7278 152.3101 Silica second lens group lens of −126.8915CX972.6391CX −41.3263 154.8530 151.8327 Silica second lens group lens of−626.4905CX −116.6456CC −12.0000 147.6711 136.1163 Silica second lensgroup beamspli Infinite Infinite −74.0000 137.2448 200.1127 Silica tterbeamspli Infinite 200.1128 Reflection tter beamspli Infinite Infinite74.0000 200.1127 200.1127 Silica tter first Infinite Infinite 6.0000148.6188 149.0707 Silica quarter- wave plate concave Aspheric −14.4638149.6392 Reflection mirror first Infinite Infinite −6.0000 144.8563141.2737 Silica quarter- wave plate beamspli Infinite Infinite −74.000139.3606 117.3979 Silica tter beamspli Infinite Infinite −61.000117.3979 100.5074 Silica tter second Infinite Infinite −4.5000 99.661798.4157 Silica quarter- wave plate lens of −157.8776CX 2282.2178C−13.7501 94.8267 91.8775 Silica third lens X group lens of −94.0059CX−46.6659CC −13.4850 82.8663 78.1418 Silica third lens group lens of−147.2485CX −77.8924CC −22.2075 72.7262 50.6555 Silica third lens grouplens of −159.2880CX −519.4850CC −13.8321 49.5648 39.0473 Silica thirdlens group lens of −129.3683CX −426.7350CC −6.1500 37.3816 32.4880Silica third lens group wafer Image Infinite


25. The optical reduction system as in claim 23 having a constructionaccording to the following data TABLE 5 Radius of Aperture ElementCurvature (mm) Thickness Diameter (mm) Number Front Back (mm) Front BackGlass variable Infinite Infinite 33.1000 123.0000 123.0000 Quartz waveplate reticle Infinite 62.7514 lens of −136.1154 −152.5295 16.8300120.7552 129.4354 Silica first lens CC CX group lens of −270.1396−191.8742 20.5341 132.9152 139.0377 Silica first lens CC CX group lensof −188.9000 −284.7476 17.5000 156.1938 165.6567 Silica first lens CC CXgroup lens of 433.8174 − 25.8293 173.8279 174.8334 Silica first lens CX841.5599C group X lens of −190.3251 −8413.4836 −34.4584 178.5071174.2260 Silica second CX CC lens group lens of 690.5706 −146.4997−11.8800 150.4109 141.8021 Silica second CC CC lens group lens of−265.9886 1773.5314 −24.1851 142.1851 141.2400 Silica second CX CX lensgroup lens of −244.9899 −142.8558 −11.8800 139.3290 133.8967 Silicasecond CX CC lens group beamspli Infinite Infinite −71.2800 134.3115189.7826 Silica tter beamspli Infinite 189.7826 Reflectio tter nbeamspli Infinite Infinite 71.2800 189.7826 189.7826 Silica tter firstInfinite Infinite 5.9400 142.3429 142.6707 Silica quarter- wave plateconcave Aspheric −18.5263 143.5034 Reflectio mirror n first InfiniteInfinite −5.9400 134.2788 130.9398 Silica quarter- wave plate beamspliInfinite Infinite −71.2800 130.1221 111.7247 Silica tter beamspliInfinite Infinite −60.4000 111.7247 96.1353 Silica tter second InfiniteInfinite −4.4550 95.3562 94.2064 Silica quarter wave plate lens of−127.4561 − −13.0104 90.4737 87.7002 Silica third lens CX 1398.8019group CC lens of −98.8795 −424.1302 −12.2874 80.7016 76.3270 Silicathird lens CX CC group lens of −132.0104 −70.9574 −17.8706 71.078953.4306 Silica third lens CX CC group lens of −123.1071 −585.4471−19.9496 52.6417 38.2256 Silica third lens CX CC group lens of −137.8349−292.6179 −6.0885 36.7251 31.8484 Silica third lens CX CX group waferImage Infinite 26.5000


26. An optical reduction system having an image space numerical apertureand an object space numerical aperture, from the long conjugate end tothe short conjugate end, comprising: a first lens group of positivepower; a second lens group of negative power, said second lens grouphaving an emerging numerical aperture, the emerging numerical aperturebeing substantially similar to the object space numerical aperture; abeamsplitter; a concave mirror; and a third lens group of positivepower; arranged such that radiation entering said system passes throughsaid first lens group, said second lens group, said beamsplitter, and isreflected by said concave mirror back through said beamsplitter andthrough said third lens group.
 27. The optical reduction system as inclaim 26 wherein: the emerging numerical aperture is slightly largerthan the object space numerical aperture.